Reliability of a customer's power supply is a primary concern for a utility. In order to provide reliable and continuous power, the utility tries to ensure that its equipment is always in working order. Utilities typically have generating stations, sub-stations, and telecommunications, system control and computer networks that should be operating at all times. To ensure continuous operation, many of these systems are provided with back-up power sources for providing temporary power whenever their main power sources are disrupted.
For example, a utility may have a communications network that includes microwave repeater stations that relay information between sites. These stations can be located in remote locations such as on a mountaintop, and must be provided with back-up power generation means to ensure that the station remains operational when its primary power source (e.g. commercial distribution power via ground lines) is interrupted. Typically, such stations are fitted with a back-up diesel generator and a number of lead acid batteries. When the primary power supply is disrupted, the diesel generators and batteries are activated to provide nominal A/C and D/C power for periods of time sufficient for repair crews to effect necessary repairs.
Because stations can be located in difficult-to-access wilderness locations, the stations are provided with large stores of diesel fuel and large numbers of lead acid batteries to ensure that enough back up power is available in the event repair crews are delayed in reaching the stations. Such remote stations present an environmental concern, as the large stores of diesel fuel and battery electrolyte pose a significant environmental hazard. As these locations are hard to reach, timely clean up of fuel or electrolyte spills are particularly difficult.
It is therefore desirable to minimize or eliminate the environmental risk that such stations pose by providing a back-up power source that is relatively environmentally friendly. Furthermore, such back up power source should be relatively light and compact: existing back up equipment comprising diesel generators, diesel fuel storage, and batteries tend to be relatively heavy; as access to remote stations can often only be made by helicopter, transporting such equipment and fuel tends to be expensive. Therefore, it is desirable to reduce the weight of the back up equipment and associated fuel to reduce the costs associated with constructing and maintaining such stations.
A similar need for reliable back-up power exists for utility sub-stations and generating stations. A substation serves to transform voltage from one level to another level. A power generating station generates electrical power from an energy source such as coal, gas or water. Presently, substations and generating stations are typically provided with lead-acid battery back-up systems to enable the substation and generating stations to perform a “black start” during a blackout, i.e. when power from a commercial distribution ground line is interrupted. Failures of lead-acid battery based back up systems to operate properly during blackouts have prompted utilities to examine alternative sources for back-up power.
Fuel cell technology has long been touted a commercially viable and environmentally superior alternative to internal combustion based power sources. Generally speaking, fuel cells electrochemically combine hydrogen fuel and oxidant to produce electricity, water and heat. One type of fuel cell is a proton exchange membrane (PEM) fuel cell; such fuel cells employ a membrane electrode assembly (MEA) which comprises an ion exchange membrane or solid polymer electrolyte disposed between two electrodes typically comprising a layer of porous, electrically conductive sheet material, such as carbon fiber paper or carbon cloth. The MEA contains a layer of catalyst, typically in the form of finely comminuted platinum, at each membrane/electrode interface to induce the desired electrochemical reaction. In operation the electrodes are electrically coupled to provide a circuit for conducting electrons between the electrodes through an external circuit. Typically, a number of MEAs are serially coupled electrically to form a fuel cell stack having a desired power output.
Due to their zero- or low-emission nature, and ability to operate using renewable fuels, the use of fuel cells as primary and/or backup power supplies is promising. For example, a fuel cell stack have be contemplated for service as an uninterruptible power supply for computer, medical, or refrigeration equipment in a home, office, or commercial environment. However, actual implementation of such fuel cell systems in real world applications have been very limited, as there are significant technological hurdles to overcome to ensure the fuel cell systems can effectively and reliably operate in the field. One particular challenge is to provide a cost-effective and compact fuel cell system that can be readily adapted to provide power at a site having multiple electrical devices with different voltage and current requirements.